Frames Problem

I’m updating the site for my boss, wich was made by somebody else. The site is frame based(Project Seven Frame extension) Most of the external pages that are loaded in the mainFrame don’t need any scrolling but there are a few pages that need scrolling so I have the option scroll for the mainFrame set to auto! But then I not only get a vertical scroll bar but also a horizontal one. Does anybody know how to get rid of the horizontal scroll bar!?